RNA interference or “RNAi” is a term initially coined by Fire and co-workers to describe the observation that double-stranded RNA (dsRNA) can block gene expression when it is introduced into worms (Fire et al., Nature 391:806-811, 1998). Short dsRNA directs gene-specific, post-transcriptional silencing in many organisms, including vertebrates, and has provided a new tool for studying gene function. This technology has been reviewed numerous times recently, see, for example Novina, C. D., and Sharp, P., Nature 2004, 430:161, and Sandy, P., et al., Biotechniques 2005, 39:215, hereby incorporated by reference.
The mucosal surfaces at the interface between the environment and the body have evolved a number of protective mechanisms. A principal form of such innate defense is to cleanse these surfaces with liquid. Typically, the quantity of the liquid layer on a mucosal surface reflects the balance between epithelial liquid secretion, often reflecting anion (Cl− and/or HCO3−) secretion coupled with water (and a cation counter-ion), and epithelial liquid absorption, often reflecting Na+ absorption, coupled with water and counter anion (Cl− and/or HCO3−). Many diseases of mucosal surfaces are caused by too little protective liquid on those mucosal surfaces created by an imbalance between secretion (too little) and absorption (relatively too much). The defective salt transport processes that characterize these mucosal dysfunctions reside in the epithelial layer of the mucosal surface. One approach to replenish the protective liquid layer on mucosal surfaces is to “re-balance” the system by blocking Na+ channel mediated liquid absorption. The epithelial protein that mediates the rate-limiting step of Na+ and liquid absorption is the epithelial Na+ channel (ENaC). Alpha-ENaC is positioned on the apical surface of the epithelium, i.e. the mucosal surface-environmental interface. Inhibition of alpha-ENaC mediated Na+ mediated liquid absorption may achieve therapeutic utility. Therefore, there is a need for the development of effective therapies for the treatment and prevention of diseases or disorders in which alpha-ENaC is implicated, e.g. cystic fibrosis in humans and animals, and particularly for therapies with high efficiency. One prerequisite for high efficiency is that the active ingredient is not degraded too quickly in a physiological environment.